Modelling the Population Dynamics of Root Hemiparasitic Plants Along a Productivity Gradient

Abstract

Root hemiparasitic plants interact with their host plants through parasitism and competition. The interactions can be divided into aboveground and belowground interactions. Because both groups of plants are autotrophic, they compete for light aboveground. Belowground interactions are more complex. The host plants compete for resources in the soil and the hemiparasitic plants prey on the host plants through haustoria, using the hosts as the main source of water and nutrients. In this paper, we modeled the relationship between these two plant types, extending the well-known Rosenzweig-MacArthur predator-prey model to cover both light competition and intra-specific parasitism among hemiparasites. We included a realistic relationship of carrying capacity to environmental productivity and followed model behavior on a productivity gradient. The model shows that, at very low productivities, there are only a few poor hosts and hemiparasites have no chance to persist. As productivity increases, there is a range of productivity where both plant types coexist. A further increase in productivity gets the system out of the coexistence range, and only host plants survive. This final prediction successfully explains patterns observed in empirical data, contrary to the results of an earlier, oversimplified model of the explored interaction. Comparison of various models demonstrates that the model is able to reproduce the decline of hemiparasites with increasing productivity only when competition for light is included.

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Acknowledgments

We are grateful for helpful discussions with Jakub Těšitel and Martina Petrů. We highly appreciate comments of two anonymous reviewers, which greatly improved the paper. We thank Keith Edwards for linguistic improvement of our manuscript. The research was supported by grants GAČR 206/08/H044, GAAV IAA601410805, MSM6007665801 and Z50070508. Access to the MetaCentrum computing facilities provided under the research grant MSM6383917201 is highly appreciated.

a11 (a12) is the partial derivative of the right-hand side of the host equation of model (4) according to x (y) and a21 (a22) is the partial derivative of the right-hand side of the hemiparasite equation of model (4) according to x (y).